Insecticides



United States Patent Ofi ice 3,184,378 Patented May 18, 1965 This invention relates to insecticides and is particularly concerned with atmospheric dispersions of non-volatile insecticides.

Pyrethrum and related insecticides are maximally elfective when dispersed in the air. Since thesematerials are practically non-volatile at ordinary temperatures, dispersion has been effected by mixing them with volatile liquids, which when volatilized, create aerosols. This technique is of great value in establishing a temporary high concentration of insecticide in the air, but the dispersion or aerosol begins to dissipate and oxidize immediately after the material has been released. Should the space to be treated again become infested, it is necessary to repeat the process.

The present invention is concerned with novel compositions and methods which make it possible to maintain an eiiective concentration of a non-volatile insecticide in the air in a confined space over a long period of time.

According to the invention, a non-volatile insecticide is mixed with a solid material which has a high vaporpressure at room temperature. I have discovered that, as the high vapor-pressure material sublimes, it carries the low vapor-pressure material into the air with it.

While various kinds of insecticides and various kinds of high vapor-pressure carrier materials may be employed, it is desirable in some cases to employ as a carrier material a substance which has insecticidal properties itself, and preferably one which attacks a stage of the insect life cycle not affected by the non-volatile component. For example, pyrethrins, which are effective against flying insects, may be employed with a carrier component comprising para-di-chloro-benzene, which is effective against larvae and eggs. This combination is particularly appropriate for use against moths.

Material which can be used include, as non-volatile components, the pyrethrins, allethrin, and related compounds, and, as, carrier materials, para-di-chloro-benzene, camphor and naphthalene.

Allethrin is available in relatively pure form, and, as such, does not sublime. It is, moreover, sensitive to oxidation.

Commercial pyrethrum is a solution in a petroleum solvent of pyrethr-ins, the active insecticidal substances of the pyrethrurn flower.

The solvent employed is a deodorized petroleum fraction known in the trade as Dec-base. Pyrethrum extracts are further identified according to the concentration of pyrethrins therein, for example, 20% pyrethrum is a mixture comprising 20% pyrethrins and 80% Deobase.

Pyrethrins in the form of commercial pyrethrum are not volatile. Thus, when 20% extract is exposed to the air, it loses 80% of its weight in about 100 hours, after which the weight remains constant over a long period of time. The residue which remains is a gummy substance comprising practically all of the original pyrethrins, thus indicating that it is only the Dec-base which evaporates.

I have discovered, however, that when either a commercial pyrethrum extract or pure allethrin is mixed with a relatively large amount of a sublirning substance, the entire mixture will sublime at a rate which approximates that at which the subliming material alone sublimes under the same conditions.

If the concentration of the non-volatile ingredient in the mixture is increased progressively, a critical concentration is reached; and mixtures containing more than this critical amount of non-volatile insecticide will leave behind on sublimation a residue consisting chiefly of nonvolatile constituents. I have further discovered that there is a critical concentration for each combination of volatile and non-volatile ingredients.

Examples of different combinations and different concentrations follow herebelow:

Example 1 A of 1% Pyrethrurn (20% extract) was mixed with para-di-chloro-benzene and allowed to stand on a 5" square of white broadcloth. When the para-di-chlorobenzene had completely disappeared, there remained tiny concentrated dirt spots of solid carbonaceous material which were deposited on the extenuated fibres standing off from the surface of the piece of cloth. A slight stain marked the spot where each of these dirt particles was concentrated.

The stain was a reddish-brown color at first, but after standing for 24 hours, the color turned to greenish. After another 48 hours, this color had almost disappeared, but the stained spot could still be discerned. After a week, the stain had disappeared almost completely. The dirt particles remained.

Example II The experiment of Example I was repeated with of 1% pyrethrum (20% extract). The results were substantially the same, although the staining was initially less extensive and disappeared within 72 hours.

Example III The experiment of Example I was repeated with of 1% pyrethrum (20% extract). When the paradichloro-benzene had completely disappeared, the cloth was entirely free of stain and the only trace of the original material was a very few small dirt spots adhering to the cloth so loosely that they were easily brushed off.

The above experiments established that the critical concentration of pyrethrins in para-di-chloro-benzene is .01%. That is, as much as .01% pyrethrins calculated on the total weight of the mixture can be Sublimated by para-di-chloro-benzene.

The result of similar experiments with other combinations are tabulated herebelow:

Critical Concentration, percent Non-volatile Ingredients Volatile Ingredients Allethrin Para-di-chloro-benzcnc.

It will be understood that the critical concentrations above set forth establish upper limits on the percentage of non-volatile ingredients which may be employed in mixtures intended for specific applications, but that higher concentrations may be used for other purposes.

For example, when the material is to be placed in direct contact with clothing or other material to be protected, i.e by sprinkling the mixture in a trunk or similar container, the concentration should be kept below the critical amount in order to avoid staining the fabric.

On the other hand, the mixture may be packed in a container having an opening of appropriate size and the entire package placed in a closet or other storage space. For such applications, the concentration of non-volatile described above., I g h 7 Indeed, the concentrations establ' hed by thismethod are-of the same order as thoseestablished temporarily.

t s 3.. p 7 ingredients may be greater than the critical amount, since any residue will remain in'the package." 7

However, I have found that mixtures containing the criticalamountjof non-volatile insecticides or less are en-1 tirely elfective' for ordinary purposes, including the treatment of enclosed spaces by sublimatio'n frontal package as through the use of aerosols.

For example, a typical aerosohbomh contains i4%f pyrethrin's. A sevenjsecond spray from such} abomb vaporizes a total of 3.5 grams ofmaterial and felfe ctively treats 1,000 cu. ft. of space. An effective concentration of pyrethrins is thus .000014 gram per cu; ft.

terialmay be placed ina confined space, such as a closet or storage room; or the material may be blowninto the fspace and/ or onto the garments by an air stream generated in a vacuum :cleaner, as is well known in the art.

I claim: a

I a 1. A, solid insecticide comprising essentially in admixture a jrirst'ingredientcomprising a 20% mixture of a pyrethrin and petroleum solvent, and a second ingredient comprising crystallinefpara-diachloro-benzene, the first ingredient comprisingfroni 01% -to-.02%' of thetotal.

2. Asolidinsecticide having the composition: 5 gram fof a,20% pyrethrurn, 80%fpetroleum solvent mixture;

A para-jdi-chloro-benzene to make up 500 grams.

One pound of a mixture of paracli-chltaro-benzene and of 1% pyre thrum (20% extract) contains .0453? One pound of the mixture when gram of pyrethrins. packaged to'sublime completely in 60 days,'will therefore release an average of .00075. gram of ,pyrethrins' each day. This amounts 'to'aOOOOlS; gram per cu. ft., in a f storage space having a volume of 50 cu. it. I

Pyrethrins like allethrin, are very sensitive'to oxidation and when exposed to the air either in the, form of extract I or in aerosols are quickly oxidized and rendered useless. I have found however that the .vapor of thefvola tile constituent in mixtures 'preparedin accordance with the invention blankets thenon-volatileconstituent and.

protects it from oxidation, at leastluntil itfi's volatilized. Since the'volatilized material is continuously replaced 'by newly sublimed material, the air in the space being treated is always supplied with 'fresh unoxidized material in an amount sufficient to kill all flying insects. I .1

The material prepared inaccordance' with the invention may be used in a plurality of ways. 'As above mentioned, the mixture may be manually scattered over thegarments or other objects to be protected; an opened package of ma- 1 "-iReferences Citedby the Examiner UNIiTED S TATESWPATENTS 7 OTHER REFERENCES I Bourcartz; Insecticides, Fungicides, and Weed Killers, 2nd ed.,:1925, pages 407--4l0.v I

35 LEWIS G O'ITS,.Primary Examiner. Y Y

DONALD}. ARNOLD, WILLIAM B. KNIGHT, i MORRIS 0. woL-K, Examiners; 

1. A SOLID INSECTICIDE COMPRISING ESSENTIALLY IN ADMIXTURE A FIRST INGREDIENT COMPRISING A 20% MIXTURE OF A PYRETHRIN AND PETROLEUM SOLVENT AND A SECOND INGREDIENT COMPRISING CRYSTALLINE PARA-DI-CHLORO-BENZENE, THE FIRST INGREDIENT COMPRISING FROM .01% TO .02% OF THE TOTAL. 